Two-stage evaporation system comprising an integrated liquid supercooler and a suction vapour superheater according to frequency-controlled module technology

ABSTRACT

The aim of the invention is to improve a refrigerating installation in such a way as to achieve high operating reliability, and savings in terms of energy and cost, in cooling circuits containing a cooling agent (cooling sols). To this end, disclosed is a refrigerating installation provided with frequency-controlled cooling units in the form of modules comprising an integrated two-stage evaporator provided with a liquid supercooler and a suction vapour superheater.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Cooling and freezing plants, refrigeration technology, refrigerationmachine for cooling and heating operation, refrigeration plants,refrigeration sets, heat pumps, energy recovery, waste heat utilization:modular technology which is used to cool and/or heat various media, suchas liquids, air, gases and other energy carriers.

2. Description of Related Art

Frequency-controlled refrigerant compressors, refrigeration sets,supercooling, energy storage are known individually but not incombination as proposed here, and in this combination it is also notknown to use the newly discovered two-stage evaporator with integratedliquid supercooling and suction steam superheating, which is alsoapplied for as part of the patent.

The prior art has disclosed plants with single-stage supercooling,suction steam superheating, direct evaporation plants for refrigerant,heat-transfer medium cooling plants (secondary coolers), cascade coolingplants, booster cooling plants, cooling plants with dry expansion (dryevaporator), thermosyphon systems (flooded evaporators) andrefrigeration sets.

The use of frequency-controlled refrigerant compressors, modularstructure of refrigeration sets, supercooling and energy storage havenot hitherto served to allow the use of such small refrigerantcompressors as those proposed here and thereby to cover very high powerpeaks in terms of the required refrigeration demand directly via themechanical refrigeration power that is generated.

Only the combination of two-stage evaporation with integrated liquidsupercooling and suction steam superheating (4/5) isfrequency-controlled modular technology (10/11) with multistagesupercooling (6) guarantees that the following objectives are achieved.

SUMMARY OF THE INVENTION

It is an object of the invention, in cooling/freezing plants,refrigeration machines for cooling and heating operation, refrigerationplants, refrigeration sets, heat pumps and all plants using refrigerantand refrigeration-transfer media, to achieve the following objectives:low energy consumption, high operational reliability, high availabilityof the refrigeration, low maintenance costs, rapid reaction time (untilthe damage is eliminated, irrespective of the nature of the damage),simple plant technology, simple system structure, low investment costs,protection of investment, high versatility (with regard to products,refrigerant, etc.)

To drastically increase the COP values and operational reliability, todrastically reduce the maintenance, operating and investment costs, thepossibility of using very small refrigerant compressors (1) in relationto the maximum refrigeration power which can be released, to generatethe refrigeration power over the majority of the duration of a standardcooling process with very high levels of efficiency and very lowrefrigerant compressor powers and thereby to cover very highrefrigeration power peaks (ratio of minimum demand to average demand andmaximum demand for refrigeration power considered over a short or longperiod of time).

Furthermore, the above objectives are to be achieved with a very smallnumber of components (9) and auxiliary refrigeration substances beingused and a minimum of refrigerant being required.

To generate and store (12) the refrigeration energy at times at whichlittle refrigeration energy is required (27).

To use this energy (27) to cover peak refrigeration powers and therebyto obtain a more uniform outlay on and demand for energy and moreuniform operating states (longer run times with fewer ON/OFF cycles ofthe compressors).

The invention is based on the combination and further development of theabove systems in refrigeration plants (11) which are of modular design(refrigeration sets).

We understand the term modular technology (11) (refrigeration sets) asmeaning a refrigeration plant which is ready to connect for each module(11) (refrigeration set), the modules (11) being connected in parallelwith one another to form a refrigeration system.

Different power levels of modules (11) are used, and it is possible fora plurality of modules (11) to be connected to a refrigeration system.

Depending on demand, it is possible for a system to start with one ormore modules (11) and for further modules (11) to be added at a laterstage.

It is possible for a plurality of systems to be combined with oneanother, and the individual modules (11) are portable and ready forconnection.

The use of frequency control (11) and the fact that the modules (11) areconnected in parallel make it possible to cover peak loads for processesthat are currently standard with significantly smaller refrigerantcompressors (1).

The refrigerant compressor power is significantly increased by the useof a special, two-stage evaporator with integrated liquid supercoolingand suction steam superheating (4/5).

The modular technology (11) increases the availability of therefrigeration that is generated significantly compared to standardindividual or compound plants.

In the event of a refrigeration module (11) failing, the refrigerationpower which it is no longer producing is partially or completelycompensated for by increasing the rotational speed of the otherrefrigerant compressors (frequency control) (10).

The use of the special two-stage evaporator technology with integratedliquid supercooler/suction steam superheater (4/5) and a two-stage ormultistage supercooling (6) has enabled us to generate and store (12/27)some of the refrigeration power required during times at which there islittle demand for refrigeration and to increase the power by means ofthe external supercooling stage (6/27) to cover peak loads at times ofhigh demand for refrigeration, without a lower evaporation temperature(31) being required during storage.

The stored refrigeration energy (12/27) in this case serves for theliquid supercooling of the refrigerant (external supercooling) (6/27).

Other energy sources can likewise be used for refrigerant supercooling(6).

A further stage of the liquid supercooling of the refrigerant isrealized by means of evaporation of the refrigerant and suction steam ofthe refrigeration plant (internal supercooling) (5).

The invention of this evaporation process with liquid supercooling andsuction steam superheating (4/5) is based on the following:

Dry expansion systems (dry evaporator) with injection valve, in which asuperheated and gaseous refrigerant leaves (20) the evaporator, areknown.

Thermosyphon systems (flooded evaporator), in which liquid refrigerantis passed into the evaporator and superheated, gaseous ornon-superheated refrigerant provided with liquid fractions flows into aseparator, and from there is passed in gaseous form without liquidfractions to the refrigerant compressor, are known.

Refrigeration systems in which heat exchange between gaseous and liquidrefrigerant is realized in order to supercool the liquid and tosuperheat the suction steam (liquid/suction steam heat exchanger) areknown.

Combinations with waste heat utilization and cascade refrigerationplants are known.

What is novel in our invention is that an evaporation system with dryexpansion is used as flooded evaporator (4), in which the refrigerantleaves (21) the evaporator with liquid fractions in the first stage.

A further novelty of our invention is that the refrigerant enters asecond evaporation stage (5/21) (dry evaporator) as a liquid/gas mixturewith a high gas fraction, and in this second evaporation stage residualevaporation takes place with subsequent high superheating of therefrigerant (22) and simultaneous supercooling of the liquid refrigeranton the second side of the heat exchanger (23).

A further novelty of our invention is that the expansion valve (2) used,which is installed outside or inside the evaporator, limits the level ofthe suction vapor temperature at the inlet of the refrigerant compressor(1/22) and at the same time controls the power of the internalsupercooling (5/23) as a function of the available evaporator power(5/24) of the first stage (4/25).

A further novelty of our invention is also the interaction of all thesecomponents, such as modular design (11) (refrigeration set), frequencycontrol of the refrigerant compressors (10), parallel connection of therefrigerant compressor cycles, two-stage evaporation with internalliquid supercooling and suction steam superheating (4/5), two-stage ormultistage supercooling (5/6), shift and storage of the refrigerationenergy from times of low demand to times of high demand (12/27),integrated waste heat utilization (7/8), with higher temperatures forwaste heat utilization (7/8/26) being available on account of theinternal supercooling (5/23).

Combinations of all types of waste heat utilization, cascade andemergency operation at module, plant or system level are possible.

The demand imposed on the modular technology (11) are an extremely highoperational reliability, low operating costs, low maintenance costs,simple plant engineering, ease of adapting power to the refrigerationpower required (expansion possibilities) and simple and flexibleadaptation to possible waste heat utilizations (7/8).

Energy saving at three levels is realized through multistagesupercooling (5/6), through power shift (for example from day to night(12/27)) and through frequency control (10), all of which leads to lowoperating costs.

Additional optimizations to the operating costs are achieved by lowerliquefaction temperatures at night, by higher evaporation temperatures(cold brine temperature rise), by higher gas outlet temperatures (wasteheat utilization (7/8/26)), by better efficiencies (over-dimensionedplants do not operate optimally in the part-load range).

Further operating cost optimizations are the negligible pressure dropsin the lines, a possible partial current shift (from day to night)(12/27), which is not at the expense of a lower evaporation temperature(31), a uniform run time of the refrigerant compressors (1)—few on/offcycles, which is additionally boosted by the generation of thesupercooler power (6/27) at night (permanent operation of therefrigerant compressors (1) is desired, depending on the process), lowand reduced start-up current on account of the small number of on/offcycles, frequency converter (10) and smaller refrigerant compressors(1), and high COP values (ratio of electrical energy to refrigerationenergy).

When failure of only part of the system occurs, the remaining modules(11) take over responsibility for some of the refrigeration power whichis missing in the event of a module failing via frequency conversion(10).

Rapid reaction time in the event of part of a plant failing, since theentire module (11) can be exchanged and the repair carried out in theworkshop.

Simple plant engineering (11) since there is no need for anyspecialists.

High availability on account of a plurality of modules (11)(refrigeration sets).

In the event of the ice store (12/27) failing, emergency cooling for thesupercooling (6/27) is realized, for example, using mains water.

In the event of the recoolers (13) failing, emergency cooling for theliquefiers (3) is realized, for example, using mains water.

Extremely small refrigerant compressors (1) in order to cover a requiredpeak refrigeration power significantly simplify the refrigeration plantengineering.

In addition, there are the advantages of smaller recoolers (13), thefact that no oil and refrigerant shifts are possible, a low oil andrefrigerant content, a small number of items of refrigeration apparatus(9), more simultaneous waste heat utilization (7/8), integration offreezing plants which is possible at any time (cascade operation),emergency cycles (supercooling 6/27)/condensation (3)) which arerealized outside the refrigeration cycles, suction steam temperatures atthe refrigerant compressor inlet (1/22) and liquid blasts which areunder control.

Small system units (11) (refrigeration set) have small components(9/1/2/etc.) and therefore low component prices, short shutdown timesand a high availability of components of this type.

In the event of a module (11) failing, the other modules (11) take overresponsibility for some of the missing refrigeration power via frequencyconversion (10).

Short reaction times for eliminating a fault, since standardized modules(11) are held in stock.

Longer service life of the refrigerant compressors (1) on account of asmall number of on/off cycles.

Basic supply can be extended on demand if the infrastructure (lines,etc.) are installed for the final size.

The site at which the plants are located can be changed without problemson account of the fact that the modules (11) (refrigeration sets) areportable.

The plants are made independent of product by virtue of the fact thatmodules can be constructed using different components (refrigerant,refrigerant compressor (1), heat exchanger (3/4/5/6/7/8), etc.).

Regulations relating to pressure, refrigerant, filling quantities, etc.can be satisfied in a simpler and more efficient way using small units(11) produced in workshops.

Further investment advantages are simple plant engineering (11) and thefact that specialists are not required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Minimum possible solution with two independent heat exchangers(4/5)

FIG. 2: Minimum possible solution with two-stage supercooling (6/5)

FIG. 3: Possible additional components per module (7/8/9, list notexhaustive)

FIG. 4: Possible system incorporation (one possible variant, notexhaustive)

FIG. 5: A combined-cycle plate-type heat exchanger (3/4/5/6/7/8) astwo-stage evaporator (4/5) with integrated liquid supercooling (5) andsuction steam superheating (5), liquefier/condenser (7),liquefier/-condenser (8), liquefier/recooler (3) and supercooler firststage (6) and with external or internal injection valve (2).

FIG. 6: New development of a combined-cycle plate-type heat exchanger(3/4/5/6/7/8) as two-stage evaporator (4/5) with integrated liquidsupercooling (5) and suction steam superheating (5), liquefier/condenser(7), liquefier/-condenser (8), liquefier/recooler (3) and supercoolerfirst stage (6) and with internal injection valve (2) of differentdesign.

FIG. 7: A combined-cycle plate-type heat exchanger (3/4/5/6/7/8) astwo-stage evaporator (4/5) with integrated liquid supercooling (5) andsuction steam superheating (5), liquefier/condenser (7),liquefier/-condenser (8), liquefier/recooler (3) and supercooler firststage (6) and with internal injection valve (2) of different design.

FIG. 8: A two-stage plate-type evaporator (4/5) with integrated liquidsupercooling (5) and suction steam superheating (5) with external orinternal injection valve (2).

FIG. 9: A two-stage plate-type evaporator (4/5) with integrated liquidsupercooling (5) and suction steam superheating (5) with external orinternal injection valve (2) of different design.

FIG. 10: Diagram illustrating the physical relationships.

DETAILED DESCRIPTION OF THE INVENTION

A refrigeration module (refrigeration set) (11) substantially comprisesone or more:

liquefiers (3), liquid supercoolers (6), liquid supercoolers/suctionsteam superheater evaporators (5) (dry evaporator second stage),evaporators (4) (flooded evaporator, first stage), refrigerantcompressors (1), injection valves (2), frequency converters (10),refrigerant, auxiliary refrigeration substances and oil (9).

A module (11) (refrigeration set) optionally additionally includes oneor more condensers (7/8), one or more waste heat utilization exchangers(7/8), further supercoolers, viewing windows (9), driers (9), filters,valves, safety equipment, shut-off equipment, collectors (9), oil pumps,distribution systems (9), electrical and control parts (9), auxiliaryrefrigeration substances, etc.

The heat exchangers (3/4/5/6/7/8) can be piped up as individualcomponents or designed as combined heat exchangers.

The injection valve (2) is mounted upstream of the evaporator (4) or inthe evaporator (4/5) (first evaporation stage).

If the injection valve (2) is mounted upstream of the evaporator (4),the measured value for limiting the suction steam is taken at thesuction line leading to the refrigerant compressor (1/22).Alternatively, the measured values for the supercooled liquid (28), thehigh pressure upstream of the injection valve (2/29) and the suctionsteam pressure downstream of the injection valve (2/30) are likewiseavailable for controlling the two-stage evaporator with integratedliquid supercooler/suction steam superheating (4/5).

At the minimum, the following components (in accordance with drawingFIG. 1) are sufficient to construct a module (11): refrigerantcompressor (1), liquefier (3), two-stage evaporator with integratedliquid supercooler/suction steam superheater (4/5), injection valve (2),refrigerant, auxiliary refrigeration substances (9), frequency converter(FIGS. 4; 10), lines and electrical control means.

A significant increase in power is achieved by connecting one or moresupercooling stages (FIGS. 2; 6) upstream of the integrated supercooler(5).

All other combinations of components (drawing FIGS. 3 and 4 as example)serve only to adapt to specific refrigeration processes and areconsidered to be known and to form part of the prior art.

A liquid fraction on the evaporator side in the second stage (5/32)directly influences the level of supercooling in the second stage (5/23)of the refrigerant liquid. The process is designed in such a way thatthe power maximum is always to the benefit of the evaporation stage 1(4/25), i.e. of the medium that is to be cooled (cf. diagram in FIG.10).

There is provision for operation with storage of the supercooling energy(FIGS. 4; 12), in which only the internal supercooler stage (stage two)(5/23/24) is used and operation for peak load, in which the storedsupercooler energy (12/27) can be deployed for liquid supercooling stageone (6/27) (liquid supercooling stage two (5/23/24) remains inoperation) and therefore alone or together with the frequency conversion(FIGS. 4; 10) to cover a peak load.

1. A refrigeration plant of modular design comprising: one or moreliquefiers, supercoolers, two-stage evaporators with integrated liquidsupercooler and suction steam superheater, injection valves, refrigerantcompressors, frequency converters, lines, refrigerant and auxiliaryrefrigeration substances, wherein on account of the modular designreliability of the refrigeration system is high, the refrigerantcompressor covers peak power by means of a frequency conversion, powerof the refrigerant compressors is increased by the two-stage evaporatorwith multistage supercooling and suction steam superheating, energy forrefrigeration generation is saved and shifted, and high operationalreliability and availability of the refrigeration energy are achieved.2. The refrigeration plant as claimed in claim 1, wherein a modulecomprises one refrigerant compressor, one liquefier, one two-stageevaporator with integrated liquid supercooler and suction steamsuperheater, one injection valve, lines, auxiliary refrigerationsubstances and refrigerant filling.
 3. The refrigeration plant asclaimed in claim 1, wherein a supercooler is connected upstream of thetwo-stage evaporator with integrated liquid supercooler and suctionsteam superheater.
 4. The refrigeration plant as claimed in claim 1,wherein one or more condensers/liquefiers for waste heat utilization isconnected downstream of the refrigerant compressor.
 5. The refrigerationplant as claimed in claim 1, wherein a module or a plurality of modulesare assembled in parallel to form a refrigeration system.
 6. Therefrigeration plant as claimed in claim 1, wherein the refrigerantcompressor delivers a mass flow required for a defined refrigerationpower via the frequency converter.
 7. The refrigeration plant as claimedin claim 1, wherein the supercooler is connectable as a function of ademand for refrigeration.
 8. The refrigeration plant as claimed in claim1, wherein the refrigeration energy for the supercooler is temporarilystored.
 9. The refrigeration plant as claimed in claim 1, wherein therefrigeration energy for the supercooler originates from independentsources.
 10. The refrigeration plant as claimed in claim 1, wherein themodular design requires only a small number of items of equipment andauxiliary refrigeration substances.
 11. The refrigeration plant asclaimed in claim 1, wherein the modular design requires only a smallquantity of refrigerant.
 12. The refrigeration plant as claimed in claim1, wherein there is no significant pressure drop in the refrigerationline.
 13. The refrigeration plant as claimed in claim 1, wherein thetwo-stage evaporator with multistage supercooling and suction steamsuperheating is also used as a separate unit in all other refrigerationplants.
 14. The refrigeration plant as claimed in claim 1, whereinrefrigeration powers and a ratio of energy input to energy output aresignificantly greater at the refrigerant compressors.
 15. A method foroperating a refrigeration plant of modular design as set forth in claim1, comprising the step of flowing a refrigeration-transfer medium on oneside through a first stage of the two-stage evaporation with multistagesupercooling and suction steam superheating.
 16. A method for operatinga refrigeration plant of modular design as set forth in claim 1,comprising the step of flowing a refrigeration-transfer medium throughthe liquefier/recooler.
 17. A method for operating a refrigeration plantof modular technology as set forth in claim 1, comprising the step ofpassing a refrigerant through one or more refrigerant compressors,liquefiers, supercoolers, two-stage evaporators with liquid supercoolingand suction steam superheating via injection member(s), through thetwo-stage evaporator with liquid supercooling and suction steamsuperheating back to the refrigerant compressor, thereby maintaining acycle.
 18. A method for operating a refrigeration plant of modulartechnology as set forth in claim 1, comprising the step of maintainingan evaporation temperature, on account of the use of the two-stageevaporator with multistage supercooling and suction steam superheating,close to an outlet temperature of a medium that is to be cooled, andconsequently similar to that achieved in thermosyphon operation andbetter than that achieved in dry expansion operation.
 19. A method foroperating a refrigeration plant of modular technology as set forth inclaim 1, comprising the step of causing a level of suction steamsuperheating up to a usable limit of the refrigerant compressor by a useof the two-stage evaporator with multistage supercooling and suctionsteam superheating.
 20. A method for operating a refrigeration plant ofmodular technology as set forth in claim 1, comprising the step of adefined power always maintaining an identical mass flow through thetwo-stage evaporator with liquid supercooling and suction steamsuperheating on both refrigerant sides.
 21. A method for operating arefrigeration plant of modular technology as set forth in claim 1,comprising the step of creating a direct link and an optimum for anevaporator power of a first evaporator stage taking account ofsupercooling upstream of the injection valve and the liquid fraction inthe refrigerant at the outlet from the first evaporator stage, which issimultaneously the inlet to a second evaporator stage.
 22. A method foroperating a refrigeration plant of modular design as set forth in claim1, comprising the step of providing operation with two-stage ormultistage supercooling and operation only with internal supercooling.